1. Field of the Invention
This invention relates to an optical apparatus having a visual axis detecting device, and particularly to an optical apparatus, for example, a camera, having a visual axis detecting device utilizing the reflected image of an eyeball of the observer (photographer) obtained when the eyeball surface is illuminated, to detect the eye gaze point or the axis in the direction of the eye gaze point, the so-called visual axis, which the observer is observing through a finder system on an observation plane (focal plane) on which an object image by an observation system is formed.
2. Related Background Art
There have heretofore been proposed various apparatuses (for example, eye cameras) for detecting which position on an observation plane the observer is observing, i.e., detecting the so-called visual axis.
For example, in Japanese Laid-Open Patent Application No. 61-172552, a parallel light beam from a light source is projected onto the front eye part of an eyeball of the observer and the visual axis is found by the utilization of the imaged positions of the corneal reflection image by the reflected light from the cornea and the pupil. Also, Japanese Laid-Open Patent Application No. 64-241511 by the assignee of this application discloses a device for detecting the direction of the visual axis.
FIGS. 12A and 12B of the accompanying drawings illustrate a conventional visual axis detecting method, FIG. 12A being a schematic view of the essential portions of a visual axis detecting optical system, and FIG. 12B being an illustration of the intensity of an output signal from the photoelectric element array 6 of FIG. 12A.
In FIG. 12A, the reference numeral 5 designates a light source such as a light emitting diode which emits infrared light not sensed by the observer. The light source 5 is disposed on the focal plane of a light projection lens 3.
The infrared light emitted from the light source 5 is collimated by the light projection lens 3, is reflected by a half mirror 2 and illuminates the cornea 21 of an eyeball 201. At this time, the reflected image of the light source (virtual image), via part of the infrared light reflected by the surface of the cornea 21, is transmitted through the half mirror 2, is condensed by a light receiving lens 4 and is re-imaged at a position Zd' on a photoelectric element array 6.
Also, light beams from the end portions a and b of an iris 23 form the images of the end portions a and b at positions Za' and Zb' on the photoelectric element array 6 through the half mirror 2 and the light receiving lens 4. Where the angle of rotation .theta., which is the angle formed by the optical axis M of the eyeball with respect to the optical axis L of the light receiving lens 4, is small, when the coordinates of the end portions a and b of the iris 23 are Za and Zb, the coordinates Zc of the central position of a pupil 24 are expressed as EQU Zc.apprxeq.(Za+Zb)/2.
Also, the Z coordinates of the corneal reflection image d and the Z coordinates of the center of curvature O of the cornea 21 coincide with each other and therefore, when the Z coordinates of a position d at which the corneal reflection image is created are Zd and the distance from the center of curvature O of the cornea 21 to the center C of the pupil 24 is L.sub.OC, the angle of rotation .theta., which is the angle formed by the optical axis M of the eyeball with respect to the optical axis L substantially, satisfies the following relational expression: EQU L.sub.OC *SIN.theta..apprxeq.Zc-Zd (1)
Therefore, in calculation means 9, the positions of particular points (the corneal reflection image d and the end portions a and b of the iris) projected onto the surface of the photoelectric element array 6 as shown in FIG. 12B are detected, whereby the angle of rotation .theta. of the optical axis M of the eyeball 201 can be found. At this time, expression (1) is rewritten as follows: ##EQU1## where .beta. is a magnification determined by the position of the eyeball relative to the light receiving lens 4, and * indicates multiplication.
Now, it is known that the optical axis M of the eyeball of the observer does not coincide with the visual axis. In Japanese Laid-Open Patent Application No. 64-274736, it is disclosed that the correction of the angle between the optical axis of the eyeball of the observer and the visual axis is effected to thereby detect the visual axis. Therein, the angle of rotation .theta. of the optical axis of the eyeball of the observer in the horizontal direction is calculated, and when the corrected value of the angle between the optical axis of the eyeball and the visual axis is .beta., the visual axis .theta.H of the observer in the horizontal direction is found as EQU .theta.H=.theta..+-..delta. (3)
As regards the signs .+-., when the angle of rightward rotation with respect to the observer is positive, the sign + is selected if the observer's eye looking into the observation apparatus is the left eye, and the sign--is selected if the eye is the right eye.
Also, in FIG. 12A, there is shown an example in which the eyeball of the observer rotates in the Z-X plane (for example, the horizontal plane), but detection is likewise possible also in the case where the eyeball of the observer rotates in the X-Y plane (for example, the vertical plane).
However, the component of the visual axis of the observer in the vertical direction coincides with the component .theta.' of the optical axis of the eyeball in the vertical direction and therefore, the visual axis .theta.V in the vertical direction is EQU .theta.V=.theta.' (4)
FIG. 13 is a view of the optical system when the visual axis detecting device of FIG. 12 is-applied to a portion of the finder system of a single-lens reflex camera.
In FIG. 13, the object light transmitted through a photo-taking lens 101 is reflected by a jump-up mirror 102 and is imaged near the focal plane of a focusing screen 104. Further, the object light diffused by the focusing screen 104 enters the eye point 201a of the photographer through a condenser lens 105, a pentaprism 106 and an eyepiece 1 having a light dividing surface 1a.
The visual axis detecting optical system is comprised of illuminating means comprising a light source 5 such as an infrared light emitting diode not sensed by the photographer (observer) and a light projection lens 3 and having an optical axis N, and light receiving means comprising a photoelectric element array 6, a half mirror 2 and a light receiving lens 4 and having an optical axis L, and is disposed above the eyepiece 1 having the light dividing surface 1a comprising a dichroic mirror. The infrared light emitted from the infrared light emitting diode 5 is reflected on the light dividing surface 1a and illuminates the eyeball 201 of the photographer. Further, part of the infrared light reflected by the eyeball 201 is again reflected by the light dividing surface 1a and is condensed on the photoelectric element array 6 through the light receiving lens 4 and the half mirror 2. The direction of the visual axis of the photographer is calculated in calculation means 9 from the image information of the eyeball (for example, the output signal shown in FIG. 12B) obtained on the photoelectric element array 6. That is, the point on the focusing screen 104 which the observer is observing (the eye gaze point) is found.
From the aforementioned visual axis .theta.H in the horizontal direction and the visual axis .theta.V in the vertical direction at this time, positions (Zn, Yn) on the focusing screen 104 which the photographer is seeing are found as ##EQU2## where m is a constant determined by the finder system of the camera.
If the position on the focusing screen 104 in the single-lens reflex camera the photographer is observing can be known, where for example, in the automatic focus detecting apparatus of the camera, points at which focus detection is possible are provided not only at the center of the image field but also at a plurality of locations in the image field and the photographer attempts to select one of those points and effect automatic focus detection, the trouble of manually selecting and inputting that one point is omitted and the point which the photographer is observing, i.e., the eyegaze point, is regarded as the point for effecting focus detection, and this is effective for automatically selecting the point and effecting automatic focus detection.
Generally, cameras are used by many people of all ages and both sexes, and the size of each portion of the eyeball of a photographer using a camera differs from person to person. So, in eye cameras for visual axis measurement commercially available, differences between individual users are corrected, whereby the error of visual axis detection is corrected.
In the aforedescribed visual axis detecting method, the calculation expression (2) for the angle of rotation .theta. of the eyeball includes a parameter L.sub.OC related to the size of the eyeball (the distance from the center of curvature O of the angle 21 to the center of the pupil 24). This has led to the problem that if the size of the eyeball of a person who uses a camera, i.e., the parameter L.sub.OC, deviates greatly from a value corresponding to the preset distance L.sub.OC, an error occurs between the calculated angle of rotation .theta. of the eyeball and the actual angle of rotation of the eyeball and visual axis detection accuracy is reduced.
Further, it has been found that the correction angle .delta. of expression (3) between the optical axis of the eyeball and the visual axis also differs depending on a characteristic such as the size of the eyeball of the photographer. This has led to the problem that when the correction angle .delta. has been set to a predetermined value, an error occurs between the direction .theta.H of the calculated visual axis and the direction of the actual visual axis depending on the photographer and visual axis detection accuracy is reduced.
In the eye cameras for visual axis measurement commercially available, correction of differences between individual users is effected. However, the optical axis of the eyeball of a user and the optical axis of a camera which photographs a scene which the user seems to be seeing do not coincide with each other, and this has led to the disadvantage that an index mark at which the user gaze must be kept considerably far from the eye camera and the index mark cannot be made integral with the eye camera.
Further, to effect the adjustment of the eye camera so that the position of the index mark photographed by the camera and displayed on a television monitor may coincide with the position of the visual axis detected when the user is gazing at the index mark, there is the difficulty that an assistant tester is necessary and the adjustment is cumbersome.
As one of methods of correcting for the individual differences in visual axes, usually index marks are provided at two or more locations in the finder system of a visual axis detecting device (an observation device) and the observer is made to gaze at the index marks. At that time, the coordinates of the eye gaze point detected in the visual axis detecting device are compared with the actual positions of the index marks to thereby obtain an amount of correction. At this time, the correction data of the observer is memorized in the visual axis detecting device, and the calculation of the visual axis is executed on the basis of the correction data.
However, the cornea of the human eyeball is substantially spherical within several millimeters about the point at which the cornea intersects the optical axis of the eyeball, but is of a flattened shape in the other area thereof.
Also, the illuminating light source of the visual axis detecting device is usually disposed so as to illuminate the eyeball obliquely from the sides thereof by two such light sources. Therefore, when an attempt is made to obtain the correction data of the visual axis by the utilization of the corneal reflection image, if respective light beams forming two corneal reflection images comprise light reflected on areas which are not symmetrical with respect to the optical axis of the cornea, the positions of the two corneal reflection images deviate relative to the positions when light is reflected on areas which are symmetrical with respect to the optical axis of the cornea, and in some cases, right correction data has not been obtained.
Likewise, the correction data of the visual axis is also obtained by the use of an iris image in addition to the corneal reflection images, but if respective light beams forming two partial iris images lying at the boundary between the pupil and the iris comprise light transmitted through areas which are not symmetrical with respect to the optical axis of the cornea, the positions of the two partial cornea images deviate relative to the positions when light is transmitted through areas which are symmetrical with respect to the optical axis of the cornea, and this has led to the disadvantage that right correction data is not obtained.